The invention relates to a polarization-sensitive beam splitter comprising at least one transparent wedge-shaped element of a birefringent material, and to a device for scanning a magneto-optical record carrier including such a beam splitter.
The invention also relates to a method of manufacturing a polarization-sensitive beam splitter comprising at least one transparent wedge-shaped element of a birefringent material, and to a device for scanning a magneto-optical record carrier.
A polarization-sensitive beam splitter of this type is described in United States Patent U.S. Pat. No. 4,951,274 for use in a pick-up element of a magneto-optical recording system. In this beam splitter two transparent wedge-shaped elements are used which are formed from crystalline quartz and are secured to each other in such a way that the optical axes of the elements mutually extend at an angle between 45xc2x0 and 135xc2x0. Such a beam splitter (Wollaston prism) proportionally occupies much space in the pick-up element of a magneto-optical recording system. Moreover, the quartz elements must be accurately processed and correctly shaped.
It is, inter alia an object of the invention to provide a polarization-sensitive beam splitter which is small and lightweight. The invention has for its object to provide a beam splitter which can be simply and accurately positioned in a light path in the desired manner. It is desirable to provide a beam splitter in which in transmission the orthogonally polarized light components are separated from each other, whereafter the polarized light beams mutually diverge. The invention has also for its object to provide a simple method of manufacturing such a polarization-sensitive beam splitter.
These and other objects are achieved by a polarization-sensitive beam splitter as described in the opening paragraph, which beam splitter according to the invention is characterized in that the wedge-shaped element comprises a uniaxially oriented polymer material which is formed from a cured liquid crystalline monomer composition.
In accordance with a very suitable embodiment of the polarization-sensitive beam splitter according to the invention, this beam splitter comprises two or three wedge-shaped elements having mutually different directions of orientation of the polymer materials.
A special embodiment of the beam splitter according to the invention comprises an anti-reflection grating, provided in the polymer material, on the faces of the beam splitter where the light beam enters and exits, respectively.
A device for scanning a magneto-optical record carrier according to the invention includes a beam splitter comprising a wedge-shaped element which is formed from a uniaxially oriented polymer material. The light path of the device can be made very compact due to the small dimensions of such a beam splitter.
To obtain a beam splitter having a small total thickness, it is possible to juxtapose a plurality of small wedge-shaped elements in a sawtooth structure. Also in that case pairs of two wedge-shaped elements each, with mutually different directions of orientation of the polymer materials, can be used.
According to the invention, the object of providing a method of manufacturing a polarization-sensitive beam splitter is achieved by means of a method in which two substrate plates are provided with orientation layers, whereafter the substrate plates are arranged with their orientation layers facing each other while forming a wedge-shaped interspace, whereafter the interspace is filled with a liquid crystalline monomer composition which is subsequently cured while forming a wedge-shaped element.
Subsequently, the substrate plates may be removed, if desired. If one substrate plate or both substrate plates are not removed, for example, because they are used as protections at the outer side of the beam splitter, a substrate plate having a thickness of between 0.1 and 1 mm is preferably used.
It is true that U.S. Pat. No. 5,042,925 describes a polarization-sensitive beam splitter with a polarizing layer comprising a cured liquid crystalline monomer composition, but this polarizing layer is not wedge-shaped. The known beam splitter is proportionally large and partly operates in transmission and partly in reflection. An accurate position and orientation in the light path is critical for a satisfactory operation of the known beam splitter.
In the drawings
FIG. 1 shows suitable monomers for forming a wedge-shaped element according to the invention,
FIG. 2 shows examples of the group X,
FIG. 3 shows examples of the group M,
FIG. 4 shows the structural formula of a suitable liquid crystalline monomer composition,
FIG. 5 shows a wedge-shaped element for use in a polarization-sensitive beam splitter,
FIGS. 6 and 7 show two different embodiments of a polarization-sensitive beam splitter comprising two wedge-shaped elements,
FIG. 8 shows an embodiment of a polarization-sensitive beam splitter comprising three wedge-shaped elements,
FIG. 9 shows a device for scanning a magneto-optical record carrier,
FIG. 10 shows a device for scanning a magneto-optical record carrier,
FIGS. 11a and b show two orientations of the beam splitter and detection system of the device of FIG. 10,
FIGS. 12a and b show two embodiments of an integrated PPBS cube and wedge element,
FIG. 12c shows an embodiment of an integrated PPBS plate and wedge element,
FIG. 13a shows a device for scanning a magneto-optical record carrier, and
FIGS. 13b, c, and d show embodiments of an integrated mirror and wedge element.